Apparatus and method to confine plasma and reduce flow resistance in a plasma reactor

ABSTRACT

An apparatus configured to confine a plasma within a processing region in a plasma processing chamber. In one embodiment, the apparatus includes a ring that has a baffle having a plurality of slots and a plurality of fingers. Each slot is configured to have a width less than the thickness of a plasma sheath contained in the processing region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 10/418,996 (APPM/007790), filed Apr. 17, 2003, which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to fabrication ofsemiconductor substrates, and more particularly, to plasma chambershaving a confinement ring configured to confine plasma inside thechambers.

2. Description of the Related Art

Generally, a plasma reactor is used to process semiconductor substratesto produce microelectronic circuits. The reactor forms a plasma within achamber containing the substrate to be processed. One of the processesthat is used is a dry etch process, which typically operates within avacuum vessel to allow the use of RF plasma conditions, to contain thereactive gases necessary for this process, and to prevent atmosphericcontamination of the sample during processing. Chambers in such reactorsare typically fabricated from aluminum or stainless steel and, as such,represent a potential contamination source. Other possible drawbacks toexposure of the vacuum vessel to plasma conditions include the cost ofparts wear-out, defect issues from deposited polymeric species, andvariability in the RF current paths. For these reasons, severalapproaches have been taken by etch system manufacturers to limit theextent of the plasma to a central region within the vacuum vessel and,in this way, segregate the functions of vacuum and plasma containment.This constraint on the extent of the plasma has generally been termed“confinement” of the plasma.

One approach for plasma confinement is to increase the lifetime ofelectrons to enhance the plasma efficiency by applying magnetic fieldsin magnetically enhanced reactive ion etch (MERIE) plasma reactors.While this approach allows the confinement of electrons, both ionicspecies and radical neutrals often interact with chamber walls, therebycausing contamination sputtering and defect issues from polymerbuild-up.

Therefore, a need exists for an improved apparatus to confine plasmawithin a processing region inside the plasma chamber.

SUMMARY OF THE INVENTION

Embodiments of the present invention are generally directed to anapparatus configured to confine a plasma within a processing region in aplasma processing chamber. In one embodiment, the apparatus includes aring that has a baffle having a plurality of slots and a plurality offingers. Each slot is configured to have a width less than the thicknessof a plasma sheath contained in the processing region.

Embodiments of the present invention are also directed to a plasmareactor that includes a chamber, a pedestal disposed within the chamber,a gas distribution plate disposed within the chamber overlying thepedestal, and a ring disposed inside the chamber. The ring includes abaffle having a plurality of slots and a plurality of fingers radiallydisposed between the pedestal and the chamber. Each slot is configuredto have a width less than the thickness of a plasma sheath contained ina processing region inside the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates an example of a plasma reactor that includes variousembodiments of the invention.

FIG. 2 illustrates a perspective view of the confinement ring inaccordance with an embodiment of the invention in greater detail.

FIG. 3 illustrates a cross sectional view of a confinement ring slot inaccordance with an embodiment of the invention.

FIG. 4 illustrates a cross sectional view of a confinement ring slot inaccordance with another embodiment of the invention.

FIG. 5 illustrates biasing alternate confinement ring fingers with apositive bias and the fingers between those alternate fingers with anegative bias in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a plasma reactor 100 that includesvarious embodiments of the invention. The plasma reactor 100 includes agrounded vacuum chamber 32, which may include liners to protect thewalls. A substrate 34 is inserted into the chamber 32 through a slitvalve opening 36 and is placed on a cathode pedestal 105 with anelectrostatic chuck 40 selectively clamping the substrate. The chuckpowering is not illustrated. Unillustrated fluid cooling channelsthrough the pedestal 105 maintain the pedestal at reduced temperatures.A thermal transfer gas, such as helium, is supplied to unillustratedgrooves in the upper surface of the pedestal 105. The thermal transfergas increases the efficiency of thermal coupling between the pedestal105 and the substrate 34, which is held against the pedestal 105 by theelectrostatic chuck 40 or an alternatively used peripheral substrateclamp.

An RF power supply 200, preferably operating at 13.56 MHz, is connectedto the cathode pedestal 105 and provides power for generating the plasmawhile also controlling the DC self-bias. Magnetic coils 44 powered byunillustrated current supplies surround the chamber 32 and generate aslowly rotating (on the order of seconds and typically less than 10 ms),horizontal, essentially DC magnetic field in order to increase thedensity of the plasma. A vacuum pump system 46 pumps the chamber 32through an adjustable throttle valve 48 and a plenum 56. A confinementring 50 is disposed inside the chamber 32 to confine the plasma within aprocessing region 72, which is defined inside the confinement ring 50.Various embodiments of the confinement ring 50 will be discussed in thefollowing paragraphs.

Processing gases are supplied from gas sources 60, 61, 62 throughrespective mass flow controllers 64, 66, 68 to a gas distribution plate125 positioned in the roof of the chamber 32 overlying the substrate 34and across from a processing region 72. The distribution plate 125includes a manifold 74 configured to receive the processing gas andcommunicate with the processing region 72 through a showerhead having alarge number of distributed apertures 76, thereby injecting a moreuniform flow of processing gas into the processing region 72. Anunillustrated VHF power supply, preferably operating at about 162 MHz,may be electrically connected to the gas distribution plate 125 toprovide power to the gas distribution plate 125 for generating theplasma.

Other details of the reactor 100 are further described in commonlyassigned U.S. Pat. No. 6,451,703, entitled “Magnetically Enhanced PlasmaEtch Process Using A Heavy Fluorocarbon Etching Gas”, issued to Liu etal. and U.S. Pat. No. 6,403,491, entitled “Etch Method Using ADielectric Etch Chamber With Expanded Process Window”, issued to Liu etal., which are both incorporated by reference herein to the extent notinconsistent with the invention. Although various embodiments of theinvention will be described with reference to the above-describedreactor, the embodiments of the invention may also be used in otherreactors, such as one described in commonly assigned U.S. Ser. No.10/028,922 filed Dec. 19, 2001, entitled “Plasma Reactor With OverheadRF Electrode Tuned To The Plasma With Arcing Suppression”, by Hoffman etal., and issued as U.S. Pat. No. 7,030,335, which is incorporated byreference herein to the extent not inconsistent with the invention.

FIG. 2 illustrates a perspective view of the confinement ring 50 inaccordance with one embodiment of the invention in greater detail. Theconfinement ring 50 is configured to confine plasma inside theprocessing region 72 and to reduce flow resistance across the chamber32. The confinement ring 50 includes a baffle 55 and a base 58 coupledto a bottom portion of the baffle 55. The base 58 is generallyconfigured to provide electrical grounding and mechanical strength forthe confinement ring 50. The baffle 55 defines an opening 70 at its topportion. The opening 70 is configured to receive the showerhead of thegas distribution plate 125 so that gases flowing the showerhead will beconfined within the processing region 72 inside the baffle 55. Thebaffle 55 further includes a plurality of slots 57 and a plurality offingers 59, disposed around the substrate 34. Neutrals in the plasma areconfigured to pass through the slots 57 into the plenum 56. The slots 57are designed such that the thickness or width of the plasma sheath isgreater than the width of each slot. In this manner, ions and radicalsin the plasma are prevented from passing through the confinement ring50, thereby isolating the plenum 56 from the processing region 72. As aresult, polymer build up inside the plenum 56 may be minimized and theamount of power that can be applied to generate the plasma may beincreased. In one embodiment, each slot 57 is designed with a width ofless than about twice the width or thickness of the plasma sheath. Theconfinement ring 50 may be made from a material that is electricallyconductive to provide a ground path for the RF power supply and the VHFpower supply when the plasma is in contact with the confinement ring 50.The confinement ring 50 may also be made from a material that isthermally conductive and etch resistant to minimize localized heating,contamination and process drift. For example, the baffle 55 may be madefrom silicon carbide (SiC), while the base 58 may be made from aluminum(Al).

FIG. 3 illustrates a cross sectional view of a slot 357 in accordancewith an embodiment of the invention. As shown in FIG. 3, the finger 359on each side of the slot 357 has a substantially triangular crosssection such that the width at the slot's upper surface is greater thanthe width at the slot's lower surface. For example, the width of theslot may range from about 3 mm to about 4 mm and the height of the slotmay range from about 12 mm to about 15 mm. In one embodiment, the widthat the slot's lower surface is about 3.4 mm while the height of the slotis about 13.4 mm. Another embodiment of the invention is illustrated inFIG. 4 in which the finger 459 on each side of the slot 457 has asubstantially inverted T cross section. In this manner, the slots inaccordance with various embodiments of the invention are configured toreduce the flow resistance (or the pressure drop) through theconfinement ring 50 while maintaining plasma confinement. By reducingthe flow resistance through the confinement ring 50, the process windowfor various etch applications for a given pump is improved and therequired power to operate the vacuum pumping system 46 is reduced. Ithas been observed that the confinement ring 50 in accordance withembodiments of the invention is configured to reduce chambercontamination and chamber cleaning time. It has also been observed thatthe confinement ring 50 is configured to improve pressure uniformityacross a substrate, thereby improving the overall process uniformity.

In accordance with another embodiment of the invention, one set offingers extends from an outside wall 53 of the confinement ring 50 whileanother set of fingers extends from an inside wall 52 of the confinementring 50, which is disposed around the substrate support pedestal 105.Each of the fingers extending from the inside wall 52 is positionedbetween two fingers extending from the outer wall 53. In this manner,every other finger is a finger from the same wall. In one embodiment,the fingers extending from the outer wall 53 are not in electricalcontact with the fingers extending from the inner wall 52. In thisembodiment, the fingers extending from the outer wall 53 may be biasedwith a positive bias (e.g., about 50 DC volts) and the fingers extendingfrom the inner wall 52 may be biased with a negative bias (e.g., about−50 DC volts). (See FIG. 5). In this manner, the electric field throughthe confinement ring 50 is modified so that ions and radicals in theplasma are attracted toward the fingers, thereby causing the ions andthe radicals to impinge on the fingers rather than going directlythrough the slots. As the ions and the radicals impinge on the fingers,the ions and the radicals become neutrals, which will flow through theslots into the plenum 56. In this manner, plasma confinement is furtherimproved. In yet another embodiment, a positive bias (e.g., about 100volts) is applied to each finger to increase the thickness of the plasmasheath.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for confining plasma within a processing region, comprising:providing a ring with a baffle having a plurality of slots, wherein eachslot has a width less than the width of a plasma sheath contained withinthe processing region; and confining a substantial portion of ions andradicals from the plasma inside the processing region.
 2. The method ofclaim 1, wherein the ring comprises a finger on each side of each slot,and wherein each finger comprises a substantially inverted T crosssection.
 3. The method of claim 1, wherein a width of each slot isbetween about 3 mm to about 4 mm.
 4. The method of claim 1, wherein aheight of each slot is between about 12 mm to about 15 mm.
 5. The methodof claim 1, further comprising reducing a flow resistance through thering.
 6. The method of claim 1, further comprising introducingprocessing gases from gas sources through mass flow controllers.
 7. Themethod of claim 6, further comprising flowing the processing gasesthrough a showerhead into the processing region.
 8. The method of claim7, further comprising electrically connecting the showerhead to a VHFpower source.
 9. The method of claim 8, wherein the VHF power sourceoperates at about 162 MHz.
 10. The method of claim 1, further comprisinginserting a substrate through a slit valve into a processing chamber;placing the substrate onto a pedestal; flowing a heat transfer gaswithin grooves in an upper surface of the pedestal; and generating aplasma within the processing chamber.
 11. The method of claim 10,wherein the heat transfer gas comprises helium.
 12. The method of claim10, further comprising connecting an RF power supply to the pedestal.13. The method of claim 10, further comprising generating a rotating,horizontal, DC magnetic field.
 14. The method of claim 1, wherein thering further comprises a finger on each side of the slots, wherein afirst finger extends from an inside wall of the ring and a second fingerextends from an outer wall of the ring.
 15. The method of claim 14,wherein the first finger is biased with a positive bias.
 16. The methodof claim 15, wherein the second finger is biased with a negative bias.17. The method of claim 15, wherein the second finger is biased with apositive bias.
 18. The method of claim 15, wherein a width of each slotis between about 3 mm to about 4 mm.
 19. The method of claim 15, whereina height of each slot is between about 12 mm to about 15 mm.
 20. Themethod of claim 1, wherein the ring further comprises a plurality offingers, wherein each finger has a substantially triangular crosssection.